1. Field of the Disclosure
The present disclosure relates to a mold for forming a pattern.
2. Discussion of the Related Art
Semiconductor devices and flat panel display devices include a plurality of fine patterns on a substrate. A photolithographic method is widely used to form the fine patterns on a substrate, such as wafer or glass. In the photolithographic method, a thin film to be patterned is disposed on a substrate, and a photoresist is applied to the thin film. The photoresist is exposed to light through a photo mask having predetermined patterns. The photoresist is then selectively removed by a developing process to form a photoresist pattern. The thin film is then etched using the photoresist pattern as an etching mask, and the photoresist pattern is removed. Accordingly, a desired pattern is left on the substrate after the photoresist pattern is removed.
However, the photolithographic method is a complicated process that includes exposing and developing, and utilizes an expensive photo mask or exposing apparatus. Production yields may be lowered and manufacturing costs increased as a result of the process. In addition, as patterns are formed to have narrower widths, the production yields may be lowered even further.
As an alternative to the photolithographic method, several methods, including a nano-imprint lithographic method, a soft lithographic method, a capillary force lithographic method, and a soft molding method, have been proposed. In the alternative methods, a soft mold of a high molecular elastic material may be used to form a pattern. A soft lithographic method according to the related art will be described hereinafter with reference to accompanying drawings. In particular, FIGS. 1A to 1F are cross-sectional views illustrating a method for forming a pattern on a substrate using a soft mold according to the related art.
In FIG. 1A, a thin film 11 to be patterned is formed on a substrate 10, and a resist 13 is applied to the thin film 11.
In FIG. 1B, a mold 15, which has depressed portions 17 corresponding to patterns to be formed, is disposed on the resist 13 such that the depressed portions 17 face the thin film 11. The mold 15 is pressed such that a top surface of the mold 15 contacts the thin film 11. Several forces are applied to the resist 13, such as a repulsive force FR between the mold 15 and the resist 13, a capillary force FC that causes the resist 13 to be drawn into the depressed portions 17 of the mold 15, a gravity force FG applied to the resist 13, and a frictional force or adhesion force FV between the substrate 10 and the resist 13. As a result of all these forces being applied to the resist 13, the overall force F pushing the resist 13 out into the depressed portions 17 of the mold 15 may be expressed by FR+FC−FG−FV. In the soft lithographic method, the mold 15 may be formed of a hydrophobic material so that the mold 15 has a relatively low surface energy. Conversely, the resist 13 may be formed of a hydrophilic material. Accordingly, the repulsive force FR may result from the surface properties of the mold 15 and the resist 13.
In FIG. 1C, the resist 13 of FIG. 1B is moved into the depressed portions 17 by applying pressure to the mold 15. The resist 13 in the depressed portions 17 is then cured to form resist patterns 13a. The resist patterns 13a correspond to the depressed portions 17 and are created by applying pressure to the mold 15.
In FIG. 1D, the mold 15 is removed after curing the resist 13. The resist patterns 13a remain on the thin film 11 after the curing of the resist 13 and removing the mold 15.
In FIG. 1E, the thin film 11 of FIG. 1D is etched using the resist patterns 13a as an etching mask. The etching results in the formation of patterns 11a that correspond with the resist patterns 13a. The patterns 11a are formed by patterning the thin film 11.
In FIG. 1F, the resist patterns 13a of FIG. 1E are removed by a stripping process. The removal of the resist patterns 13a leaves the patterns 11a on the substrate 10.
Generally, the separation of the mold from the resist pattern may be accomplished easier when the surface energy of the mold is lower than the surface energy of the resist. The surface energy is the energy per unit area required to interface between a solid or liquid phase material and a gas phase material. As the solid or liquid phase material has a larger surface energy, it becomes more difficult to interface with the gas phase material.
Accordingly, in the soft lithographic method, such as with an in-plane printing (IPP) method, to adequately form a predetermined resist pattern, the surface energies of the mold, the resist and the substrate, which may be referred to as γMOLD, γER and γsubstrate, respectively, should satisfy the following relation: γMOLD<γER<γsubstrate 
If the surface energy of the resist γER is lower than the surface energy of the substrate γsubstrate, the resist may be more easily applied to the substrate. If the surface energy of the resist γER is higher than the surface energy of the mold γMOLD, a repulsive force may be induced between the mold and the resist pattern, and the mold may be more easily separated from the resist pattern. Since the repulsive force of the mold to the resist increases as the surface energy of the mold γMOLD is lowered, it is advantageous for the formation of a pattern to lower the surface energy of the mold γMOLD.
Generally, polydimethylsiloxane (PDMS) may be used as a material for the soft mold of the soft lithographic method. In the PDMS mold, uncured chains come out of a surface of the mold, and the PDMS mold keeps a hydrophobic property. Additionally, since the PDMS mold has an elastic property, the PDMS mold may uniformly contact a surface of a substrate to be patterned. The PDMS mold has a relatively low surface energy, and as a result the PDMS mold can be easily detached from the substrate. However, PDMS is heat-curable, and thus the PDMS mold is cured by heat. Accordingly, when the PDMS mold is fabricated, the heat may result in deformations of the mold. In particular, changes in dimensions of mold patterns may be caused due to a shrinking transformation. In addition, PDMS has relatively high viscosity, and as a result, the PDMS material that is deposited through a dispensing method has a relatively large thickness. Further, it may be difficult to reduce the thickness of the PDMS mold.